The speed of information communication has been increasing. The use of electric signals in the information communication hinders increases in communication speed. Optical signals allows for information to be conveyed at higher speeds. Japanese Laid-Open Patent Publication Nos. 2002-258117, 2006-140233, and 10-48449 each describe an example of a photoelectric mixed substrate that includes metal wires for transmitting electric signals, optical waveguide for transmitting optical signals, light emitting elements for converting electric signals to optical signals, and light receiving elements for converting optical signals to electric signals.
In such a photoelectric mixed substrate, the superimposition of noise on the electric signal transmitted by the metal wires becomes a factor that inhibits high-speed transmission of electric signals.